cold-blooded

designating or pertaining to animals, as fishes and reptiles, whose blood temperature ranges from the freezing point upward, in accordance with the temperature of the surrounding medium; poikilothermic.

cold-blooded

adj.

also cold blooded; 1590s, of persons, "without emotion, unfeeling;" of actions, from 1828. The phrase refers to the old notion that blood temperature rose with excitement. In the literal sense, of reptiles, etc., from c.1600. From cold (adj.) + blood (n.). Related: Cold-bloodedly; cold-bloodedness.